1. Field of Invention
The invention relates to an ink jet recording apparatus, particularly to an ink jet recording apparatus and its maintenance method capable of keeping a recording head in a proper state.
2. Description of Related Art
Conventionally, an ink jet printer, for example, is known as a recording apparatus that produces records of prints by ejecting ink onto a recording medium such as paper. In the ink jet printer, there is provided an ink cartridge where ink is stored, which is replaceable from a recording head unit including a recording head. The ink is supplied from the ink cartridge into the recording head, where the ink is ejected from each nozzle to produce records.
When the user presses a predetermined switch while the ink jet printer is in operation, a maintenance operation is manually performed to keep the head in a proper state. When a predetermined condition is satisfied or the ink cartridge is replaced with a new one, the maintenance operation is automatically performed. For example, a so-called purging operation is performed. The purging operation is performed in the following manners: one is that the ink is sucked in at the end of the nozzle, that is a nozzle surface where the nozzle is open, and the other one is that the ink in the recording head is forcedly ejected through the application of pressure to an ink supply part.
The purging operation described below is an operation for removing the ink from the recording head through the use of suction via a suction cap by putting the suction cap on the nozzle surface and creating a negative pressure within the suction cap by a suction pump.
The ink jet printer, where the purging operation is performed, is capable of eliminating air bubbles or minute contaminants occurring during the purging operation from ejection channels, to thereby return the ink ejection from the nozzles to the normal state and recover the recording quality.
However, in some cases, air bubbles and minute contaminants occurring within the nozzles are not able to be fully eliminated only with the purging operation by suction through the use of negative pressure as described above. Minute bubbles and contaminants are apt to be adhered to the interior walls of the channels (not shown) and manifolds forming the ink passages, resulting in a lower velocity of ink near the interior walls. Therefore, it is difficult to eliminate bubbles and contaminants adhered to the interior walls even if the purging operation is performed. Such minute bubbles and contaminants have little effect on ink ejection when dots of small diameter are printed in a stable cycle. However, when the ink is continuously ejected at high frequencies, bubbles adhered to the walls suddenly expand or move around, resulting in an interruption of the ink ejection. In the ink jet printer, it is necessary to eject the ink in an appropriate cycle in accordance with the change of dot patterns to be printed. As a result, the recording quality is lowered because of the minute bubbles and contaminants, which are difficult to eliminate with the purging operation.
Therefore, there are some ink jet printers that eliminate the minute bubbles and contaminants as much as possible by repeating the purging operation. However, it is still hard to completely eliminate the bubbles and contaminants. In addition, the repetition of the purging operation increases the number of disposed ink cartridges that are not used for printing, which results in raised running costs and additional time till the maintenance operation is completed.
In the ink jet printer where the purging operation is performed, the ink ejected during the purging operation is adhered to the nozzle surface. When left standing, the adhered ink may have a detrimental effect on the recording head such as ink ejection failure and ink clogging. It is preferable that such ink is eliminated immediately. Therefore, after the purging operation, to wipe the adhered ink from the nozzle surface of the recording head, a wiper operation is performed by bringing a wiper into contact with the nozzle surface of the recording head and moving the recording head.
However, the ink adhered to the nozzle surface immediately after the purging operation includes a lot of minute air bubbles generated due to hard ink flow by the purging operation. Furthermore, because the ink inside the recording head is acted upon by a negative pressure (back pressure), which works in a direction to be drawn due to a porous structure of the ink cartridge as already known, some ink, including air bubbles, adhered to the nozzle surface is drawn back from each nozzle into the inside of the recording head. Therefore, the wiping operation that wipes the nozzle surface is not enough to eliminate the air bubbles, which have been drawn back into the recording head along with the ink. On the contrary, the wiping operation sometimes causes the ink, including bubbles, to get pushed back into the nozzle. In addition, when groups of nozzles for inks of various colors are provided on the nozzle surface, the wiping operation may cause different color ink to get pushed into the different nozzles.
To expel the bubbles or the different color ink from the recording head, a preliminary ejection or flushing operation can be used. In addition, bubbles or different color ink can also be ejected through the use of a high-frequency preliminary ejection.
However, when the ink is continuously ejected at high frequencies, the flow of ink is changed greatly and the meniscus in each nozzle may be destroyed, thus impeding a shift to the recording operation (so-called nozzle malfunction). On the other hand, when the ejection is performed at low frequencies, more time is needed to eliminate bubbles or different color ink, or the amount of ink to be ejected is eventually increased.
Therefore, the invention provides an ink jet recording apparatus and its maintenance method capable of restoring a recording head to a proper state and performing a maintenance method to shift to a recording operation immediately.
In an exemplary aspect of the invention, an ink jet recording apparatus comprises a head unit having a recording head that performs recording by ejecting ink onto a recording medium, a wiper mechanism that wipes the ink adhered to a nozzle surface of the recording head, and a preliminary ejection device that applies a drive voltage waveform for preliminary ejection to the recording head. In various embodiments, the preliminary ejection device comprises a first preliminary ejection drive device that generates a stable waveform which causes small fluctuations of ink pressure in the recording head, and applies the stable waveform to the recording head to cause a first preliminary ejection, a second preliminary ejection drive device that generates an unstable waveform which causes larger fluctuations of ink pressure in the recording head than the first preliminary ejection, and applies the unstable waveform to the recording head to cause a second preliminary ejection, and a control device that actuates the first preliminary ejection drive device after a wiping operation by the wiper mechanism so that the recording head performs the first preliminary ejection, and then actuates the second preliminary ejection drive device so that the recording head performs the second preliminary ejection.
In another exemplary aspect of the invention, an ink jet recording apparatus comprises a head unit having a recording head that performs recording by ejecting ink onto a recording medium, a wiper mechanism that wipes the ink adhered to a nozzle surface of the recording head, and a preliminary ejection device that applies a drive voltage waveform for a preliminary ejection to the recording head. In various embodiments, the preliminary ejection device comprises a first preliminary ejection drive device that generates a first drive voltage waveform, which causes a small amount of ink to be ejected, and applies the first drive voltage waveform to the recording head to perform a first preliminary ejection by small droplets, a second preliminary ejection drive device that generates a second drive voltage waveform, which causes a larger amount of ink to be ejected than the amount of ink at the first preliminary ejection by the small droplets, and applies the second drive voltage waveform to the recording head to perform a second preliminary ejection by larger droplets than the first preliminary ejection, and a control device that actuates the first preliminary ejection drive device after a wiping operation by the wiper mechanism so that the recording head performs the first preliminary ejection, and then actuates said second preliminary ejection drive device so that the recording head performs the second preliminary ejection.
In a further exemplary aspect of the invention, an ink jet recording apparatus comprises a head unit having a recording head that performs recording by ejecting ink onto a recording medium, a purge mechanism that forces the recording head to purge the ink therefrom by sucking the ink from an ink ejection side of the recording head or by applying a pressure to an ink supply side of the recording head, to improve an ink ejection condition, and a preliminary ejection device that generates a drive voltage waveform including at least an unstable waveform which causes fluctuations of ink pressure in the recording head, and applies the drive voltage waveform for a preliminary ejection to the recording head, the preliminary ejection device also comprising a control device that causes the recording head, that undergoes a purging operation, to perform the preliminary ejection before the purging operation by the purge mechanism.
In another exemplary aspect of the invention, a maintenance method for returning the ink ejection to an proper status in an ink jet recording apparatus, comprises the steps of wiping ink adhered to a nozzle surface by a wiper mechanism, performing a first preliminary ejection through the generation of a stable waveform as a drive voltage waveform which causes small fluctuations of ink pressure after the wiping step and the application of the stable waveform, and performing a second preliminary ejection through the generation of an unstable waveform as a drive voltage waveform, which causes larger fluctuations of ink pressure than the first preliminary ejection, and the application of the unstable waveform.
In a further exemplary aspect of the invention, a maintenance method for returning the ink ejection to an proper status in an ink jet recording apparatus, comprises the steps of wiping the ink adhered to a nozzle surface by a wiper mechanism, performing a first preliminary ejection by small droplets through the generation of a first drive voltage waveform which causes a small amount of ink to be ejected after the step of wiping by the wiper mechanism and the application of the first drive voltage waveform, and performing a second preliminary ejection by larger droplets than the first preliminary ejection through the generation of a second drive voltage waveform which causes a larger amount of ink to be ejected than the amount of ink at the first preliminary ejection by the small droplets and the application of the second drive voltage waveform.
In another exemplary aspect of the invention, a maintenance method for returning the ink ejection to an proper status in an ink jet recording, comprises the steps of performing a preliminary ejection through the generation of an unstable waveform as a drive voltage waveform which causes fluctuations of pressure in the recording head and the application of the unstable waveform to the recording head, and purging the recording head of the head unit after the step of performing the preliminary ejection.